Systems and methods have been developed for fragmentation of kidney stones and gallstones by utilizing shock waves generated by a suitable source and reflector system. Several systems and methods of this type have been devised. The technique is generally referred to as shock wave lithotripsy. The early approaches have involved immersing the patient in water and directing the shock wave, generated by an underwater spark discharge, at the stone. In such method and device, high pressure shock waves are generated by the underwater spark discharge and are focused by an ellipsoidal reflector toward the stone in the patient. When the shock waves hit the stone, pressure and tensile forces are produced that lead to its fragmentation. Such liberation of energy occurs when there is a change of acoustic impedance from water or body tissue to the stone. That is, pressure and tensile forces are created both when the shock wave enters the stone and when it leaves, and the stone starts to disintegrate into a fine grit or powder. A more recent development is the dry table system, such as the Medstone International, Inc. Model 1050ST Lithotripter System, which does not require the patient to be immersed in water for the shock wave treatment.
These shock wave systems also require the stones to be appropriately located and positioned with respect to the shock wave, and the localization systems commonly used involve X-ray imaging. Basically, the physician takes several X-rays to determine where the stone is in the body, such as a stone in the right kidney. Prior to the application of the shock waves, two oblique X-rays (head and foot) are taken and the resultant developed films are digitized. Then, through automatic computations by triangulation the location of the stone is determined with reference to the focal point of the shock wave equipment.
A description of X-ray location systems in kidney lithotripters can be found, for example, in U.S. Pat. Nos. 4,669,483 and 4,705,026.
While X-ray localization is used in the case of kidney stones, ultrasound imaging can be used in the case of gallstones and it is actually easier to find and locate gallstones through the use of ultrasound rather than X-rays. In addition, the ultrasound techniques are safer inasmuch as there does not need to be any exposure to X-rays. However, X-ray localization of such stones has continued to be used because no suitable non X-ray accurate localization technique has been developed.